The present invention generally relates to advanced coal gasification systems. In particular, the present invention relates to a continuous coal gasification system.
The gasification process involves turning coal or other carbon-containing materials into dusty gas, such as hydrogen and carbon monoxide. Because coal costs less than natural gas and oil, there is a large economic incentive to develop gasification technology. An issue with existing gasification technologies is that they generally have high capital costs and/or relatively low availability. Availability refers to the amount of time the equipment is on-line and making products. One cause for low availability is that current coal gasification systems operate as batch processes for filtering ash particles from the synthesis gas stream.
Many current coal gasification systems use downstream cyclone and candle filters for separating small micron (i.e., approximately 0.1 microns to approximately 100 microns) size ash particles from the product synthesis gas stream. The cyclones and candle filters are designed to drop solid dry ash particles in the synthesis gas stream into a bottom hopper by gravity for subsequent transfer from high pressure to ambient pressure (i.e. approximately 1000 pounds per square inch to approximately 14.7 pounds per square inch). The transfer of these dry ash particles from high pressure to ambient pressure is commonly performed with complex lock hopper subsystems. Lock hoppers are typically large in size and operate in batch mode.
While efficient, one concern with using lock hoppers is that they can produce significant transient upset conditions in a continuous gasification process. This is due to the fact that lock hoppers include a plurality of valves which must be repeatedly opened and closed. In addition, the valves are exposed to significant amounts of dry ash particles and typically have a very short lifetime due to the abrasive solids particles which continually erode the valves each time the valves are cycled. When the valves are being replaced, the gasification system must be shut down, costing valuable operating time.
By eliminating lock hoppers from the gasification system, the gasification system may be able to operate continuously, rather than in batch mode with a nominal frequency of 24 cycles per day.